Two-dimensional optical scan system using a counter-rotating disk scanner

ABSTRACT

A counter-rotating disk scanner together with another scan mechanism provides two-dimensional optical scanning. The counter-rotating disk scanner includes counter-rotating scan disks that implement the scanning action as they rotate through an optical axis of the system.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation-in-part of U.S. patent applicationSer. No. 10/750,790, “High Speed, High Efficiency Optical PatternGenerator Using Rotating Optical Elements,” filed Dec. 31, 2003 byLeonard C. DeBenedictis et al. The subject matter of the foregoing isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to two-dimensional optical scanners,such as for use in displays. More particularly, this invention relatesto two-dimensional optical scanners that use multi-faceted rotating scandisks.

2. Description of the Related Art

Two-dimensional optical scan systems can be used in a variety ofapplications. For example, they can be used to scan an optical beam overa specified area in order to generate a two-dimensional display. Asanother example, they can be used to scan the field of view of adetector (or detector array) over an external scene, thus allowing thedetector to capture a two-dimensional image of the scene. In both ofthese examples, the optical system may be required to produce ahigh-resolution image, with short exposure periods and a large imagearea to be covered. As a result, the two-dimensional scanners used inthese optical systems can be complex and/or costly.

For example, in the case of large screen HDTV displays that are suitablefor projection use in conference rooms, the high screen resolutioncombined with short frame periods and high screen brightness levelstypically results in complex and costly scan systems. One example designis described in Published U.S. Patent Application No. 2002/0050963,“Light Beam Display with Interlaced Light Beam Scanning” by Conemac andFord. This HDTV display system uses a high performance polygon scannerto produce the horizontal line raster scan. Two high performance,interlaced galvanometer scanners are used in conjunction with two arraysof high intensity laser diode sources to produce the vertical fieldscan. The laser diode sources, galvanometer scanners and polygon scannerare carefully aligned and synchronized in time in order to generate thedisplay.

As an example of electro-optical camera systems, cameras for theinfrared spectrum have been designed based on a large variety ofcomplicated opto-mechanical scan systems. Two examples are theinternal-bowl-scanner and the pyramidal polygon scanner. However, thescan resolution of these devices is limited by the limited number ofscan facets that can be placed on the scan mechanisms and by thelimitations on numerical aperture (NA) imposed by the scanning facetgeometries.

Thus, there is a need for improved two-dimensional optical scan systems,including those that are suitable for use in high-resolution (e.g.,HDTV) display systems and/or high-resolution electro-optic imagingsystems.

SUMMARY OF THE INVENTION

The present invention overcomes the limitations of the prior art byusing a counter-rotating disk scanner in conjunction with another scanmechanism to provide two-dimensional optical scanning. Thecounter-rotating disk scanner scans along one direction and the otherscan mechanism scans along a cross direction (usually, a perpendiculardirection). The second scan mechanism could be another counter-rotatingdisk scanner, or it could be a more conventional scanner such as agalvanometer, piezo-electric or polygon scanner.

In one aspect of the invention, the counter-rotating disk scannerincludes two scan disks. Each scan disk has a plurality of facets thatrotate around a rotational axis. Facets on the first scan disk havecorresponding facets on the second scan disk, and the two scan diskscounter-rotate so that the corresponding facets are synchronized as theyrotate through the optical axis of the overall optical system. Therotation of corresponding facets through the optical axis causes thescanning.

In one design, the rotational axes of the two scan disks are offset fromeach other and the optical axis of the system intersects the scan disksat a point located between the two rotational axes. The scan directionis approximately parallel to the tangential direction of the scan disks(i.e., approximately perpendicular to the line connecting the tworotational axes).

In one implementation, the facets on the scan disks include lenses andthe lenses on corresponding facets have approximately the same opticalpower. Aberrations can be corrected in a number of ways. For example,the lenses can be aspheric, with the asphericity correcting “dynamic”aberrations introduced by rotation of the facets through the opticalaxis. Furthermore, a separate lens group can correct for optical powerand/or aberrations introduced by the facets. One advantage of a designbased on counter-rotating scan disks is that corresponding facets can bedesigned to introduce scan line bows that counteract each other, so thenet bow is significantly reduced. Another advantage is that the scandisks can be rotated at high speeds.

These types of two-dimensional scan systems can be used in a number ofapplications. For example, an incident optical beam (or array of opticalbeams) can be scanned to produce a display. In one design, acounter-rotating disk scanner generates the fast scan (e.g., ahorizontal line raster scan) and a galvanometer scanner generates theslow scan (e.g., a vertical field scan). In the direction of propagationfor the optical beam, the system includes the galvanometer scanner, apre-scanner lens group, the disk scanner and a post-scan imaging lensgroup (e.g., an F-θ lens group). The pre-scanner lens group acceptsoptical beams at different incident angles, due to scanning of thegalvanometer scanner. It also corrects for optical power and aberrationsintroduced by the facets on the disk scanner. The facets themselves maybe aspheric, for example to correct for dynamic aberrations introducedby rotation of the facets through the optical beam. The post-scanimaging lens group can also correct for some of these dynamicaberrations.

Another example of a display includes a polygon scanner, a pre-scannerlens group, a counter-rotating disk scanner and a post-scan imaging lensgroup. In this example, the polygon scanner implements the fast scan andthe disk scanner implements the slow scan. The pre-scanner lens groupand post-scan imaging lens group can perform similar functions as in theprevious example.

As a final example, the two-dimensional scan system can also be used “inreverse.” Rather than scanning an incident optical beam, the scan systemcan be used to scan the field of view of a detector, thus allowingtwo-dimensional image capture. Other aspects of the invention includemethods and applications corresponding to the devices and systemsdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention has other advantages and features which will be morereadily apparent from the following detailed description of theinvention and the appended claims, when taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of a display that uses a two-dimensional scansystem according to the invention.

FIG. 1B is a block diagram of an imaging system that uses atwo-dimensional scan system according to the invention.

FIG. 2A is a perspective view of one example of a counter-rotating diskscanner.

FIG. 2B is a top view of the disk scanner of FIG. 2A.

FIG. 2C is a diagram illustrating bow correction in the disk scanner ofFIG. 2A.

FIG. 3 is a perspective view of a reflective counter-rotating diskscanner.

FIG. 4 is a perspective view of a display system using a galvanometerscanner and a counter-rotating disk scanner.

FIG. 5 is a composite cross-sectional view of the scan system of FIG. 4,illustrating scanning by the disk scanner.

FIG. 6 is a composite cross-sectional view of the scan system of FIG. 4,illustrating scanning by the galvanometer scanner.

FIG. 7 is a perspective view of a display system using a polygon scannerand a counter-rotating disk scanner.

FIG. 8 is a composite cross-sectional view of the scan system of FIG. 7,illustrating scanning by the polygon scanner.

FIG. 9 is a composite cross-sectional view of the scan system of FIG. 7,illustrating scanning by the counter-rotating disk scanner.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1B are block diagrams of two optical systems that use atwo-dimensional scan system 110 according to the invention. In thedisplay of FIG. 1A, an optical source 150 produces one or more opticalbeam(s) that are imaged by the imaging system 155 onto a display surface158. The optical train of this system also includes a two-dimensionalscan system 110 that scans the optical beam(s) to produce the displayedimage. In the imaging system of FIG. 1B, an exterior scene 168 is imagedby the imaging system 165 onto a detector (or detector array) 160. Thetwo-dimensional scan system 110 scans the field of view of the detector160 over the scene 168 in order to capture the two-dimensional image.

In both of these examples, the two-dimensional scan system 110 includesa counter-rotating disk scanner 120 and a second scan mechanism 130. Thedisk scanner 120 implements the scan along one direction 125 and theother scan mechanism 130 implements the scan along a cross direction135. The two scan directions are usually approximately perpendicular butthey can intersect at other angles (e.g., 60 degrees) depending on theapplication. Examples of other scan mechanisms include galvanometerscanners, piezo-electric scanners and polygon scanners. Other examplesmight include acousto-optic scanners or scanners based on diffractive orholographic optics. Another counter-rotating disk scanner can also beused as the second scan mechanism 130.

FIGS. 1A-1B are simplified diagrams. The systems may include additionaloptics located anywhere along the optical axis 190 for shaping and/ordirecting the optical beam(s). The orders of the different componentsmay also be changed. For example, the order of the disk scanner 120 andthe second scan mechanism 130 may be interchanged. Alternately, theimaging systems 155, 165 may include components that are interspersedamong the scanners 120, 130 and/or the source/detector 150/160. Forconvenience, the phrase “scanning the optical axis” will be used torefer to scanning in any type of application. It includes scanning anincident optical beam, as shown in FIG. 1A, as well as scanning thefield of view of some other element, as shown in FIG. 1B.

FIGS. 2A-2C show an example of a counter-rotating disk scanner. The diskscanner includes two disks 220A-220B that are counter-rotating. Eachdisk 220 has a number of facets 230, which are represented by circles inFIGS. 2A and 2B. The circle shape does not imply that the facets 230must be physically circular. For example, they may be shaped liketruncated wedges as shown in FIG. 2B. The facets on one disk 220A havecorresponding facets on the other disk. The rotation of the disks 220 issynchronized so that corresponding facets rotate through the opticalaxis 190 in synchronization. The optical axis 190 is scanned as thecorresponding facets together rotate through the beam. For convenience,the portion of each facet that produces the scanning shall be referredto as the scan component of the facet.

FIGS. 2B-2C illustrate how facets can be designed so that their radialscan effects cancel. A scan component on a single scan disk willgenerally introduce a bow in the scan line as it rotates through theincident optical beam. In FIGS. 2B-2C, while the scan component on eachscan disk may introduce a bow, the two scan components are designed sothat the different bows counteract each other and the overall bow isreduced or eliminated.

One example of a scan component is a lens. When the lens is centeredwith the optical axis 190, the axis will not be deflected. However, asthe lens rotates through the incident optical beam, the off-center lenswill produce a change in ray direction proportional to the amount ofdecenter. That is, Δθ=δx/f where Δθ is the change in ray direction, δxis the amount of decenter and f is the focal length of the lens. Thus, ascan line can be created by moving a lens through an optical axis.

Assume for the moment that there is only one scan disk 220A, that theoptical axis 190 is normally incident to the scan disk 220A and that thescan component of the current facet has the same optical effect as alens with negative optical power (positive power lenses can also beused), as represented by the circle 230. The circle representation isnot meant to imply that the scan component must be circular in shape.For example, it may have the same shape of the facet. The optical axisis aligned with the center of the circle 230. As the facet rotatesthrough the optical axis 190, the center of the circle 230 also rotatesabout the rotational axis 225A. The resulting scan line follows themotion of the lens, tracing out an arc 240A as shown in FIG. 2C. The sagof the arc is the bow of this scan line.

This bow can be reduced, or even eliminated, as follows. If the scancomponent on scan disk 220B is also a lens with negative optical power,it will trace the arc 240B. But this arc is bowed in the oppositedirection as arc 240A. The two bows counteract each other, resulting ina net scan line 245 that scans faster and is longer and with less bow.In some cases, the bow can be entirely eliminated. For example, thiswill be the case if the scan disks 220A-B are in close proximity to eachother so that propagation between the scan disks has negligible effect,the distance from the optical axis 190 to each rotational axis 225 isthe same, and both scan components are lenses with the same opticalpower located in the same relative position on their respective facets.In cases where the scan disks 220 are spaced apart, bow correction canbe achieved by small differences in the optical power of the two scancomponents.

In addition, the scan components can be designed differently for eachset of corresponding facets. For example, different facets can uselenses of different powers, which results in different length scanlines. As another example, in many cases, it may be desirable for thescan components to be the same for each set of facets, but some otheraspect of the facets may vary. In one approach, facets may include anoffset component in addition to a scan component. The offset componentoffsets the entire scan line in a direction perpendicular to the scandirection. Thus, if different facets have the same scan component butdifferent offset components, the resulting scan lines will beapproximately the same length but will be offset from one another in theorthogonal direction. For example, see U.S. patent application Ser. No.10/750,790, “High Speed, High Efficiency Optical Pattern Generator UsingRotating Optical Elements,” filed Dec. 31, 2003 by Leonard C.DeBenedictis et al., which is incorporated herein by reference. The useof offset components can produce a two-dimensional scan withoutrequirement a second scan mechanism such as a galvanometer mirror. Theresulting two-dimensional scanner can be quite compact and efficient.

The term “scan component” is distinguished from “facet” because the scancomponent may or may not be implemented as a physically distinctcomponent. For example, the scan component can be a lens that isattached to one side of the optical element 220 with a separate offsetcomponent attached to the reverse side. Alternately, it may beintegrated into a single component. For example, a general asphere maybe used, with the asphere implementing both the scanning and the offsetfunctions. It may also implement additional functions, such asaberration correction.

One advantage of the counter-rotating disk scanner is its speed. Diskscan be rotated at very high speeds. For example, if a scan disk contains30 facets and rotates at a speed of 10,000 rpm, then the system willgenerate 5,000 scans per second for a single beam source. If the sourceproduces an array of N optical beams, then 5,000N scans per second willbe generated. Furthermore, the speed can be varied. In one approach, thescan disks are driven by motors. The drive shafts or the disksthemselves are encoded and the feedback is used to both control thespeed of the disks and to synchronize the disks with each other, withthe other scan mechanism 130 and/or with other components in the system(e.g., the feed for a video signal or timing control for a detector).

As further variations, the examples shown above use transmissive facetsbut reflective or hybrid designs can also be used. The scan componentscan also be based on refraction, reflection, diffraction or acombination of these. Mirrors, conventional lenses, aspheres, Fresnellenses, kinoforms, diffractive and holographic optics are examples ofpossible physical implementations. The term “lens-like optical element”will be used to refer to refractive lenses, curved mirrors, holographiclenses and other optical elements that are counterparts to refractivelenses.

FIG. 3 illustrates a reflective design. In this example, two reflectivecounter-rotating scan disks 220A-220B are tilted relative to normal. Theoptical axis 190 is reflected by the first scan disk 220A onto thesecond scan disk 220B. Both scan disks 220 also introduce deflectionsthat generate the scanning motion. The second scan disk 220B introducesa second deflection, with counteracting bow.

FIGS. 4-6 show an example of a large format, high resolution HDTV-classdisplay system based on a dual-disk scanner. The optical train for thisexample includes a galvanometer scanner 410, a pre-scanner lens group420, a counter-rotating dual-disk scanner 430 and a post-scan imaginglens group 440. For clarity, only one facet 432A-432B from each of thescan disks is shown in FIGS. 4-6.

The dual-disk scanner 430 produces the fast scan, which typically wouldbe a horizontal line scan for most current displays. The galvanometerscanner 410 produces the slow scan, which typically would be thevertical field scan. In other words, the rotation of one pair ofcorresponding facets 432 through the incident optical beam will generateone scan line. In that time, the galvanometer scanner 410 introduces theappropriate vertical field offset to generate the next scan line.

FIG. 4 shows a single ray bundle 490 when both the galvanometer scanner410 and the dual-disk scanner 430 are in their “neutral” position (i.e.,center of the scan lines). FIG. 5 is a cross-sectional view thatillustrates scanning in the Y direction (the optical axis is along the Zdirection) by the dual-disk scanner 430. This figure shows threedifferent positions for the pair of scan components 432—neutral position(center of the scan) 432A-B(1), partway through the scan 432A-B(2), andthe edge of the scan 432A-B(3)—and the corresponding ray bundles 490,492(2) and 492(3). This illustrates one half of the fast scan generatedby the dual-disk scanner 430. Similarly, FIG. 6 is a cross-sectionalview that illustrates three scan positions for the galvanometer scanner410 and the corresponding ray bundles 490, 494(2) and 494(3). Thisillustrates one half of the slow scan in the X direction generated bythe galvanometer scanner 410.

In more detail, the scan components for the facets 432 in this designare lenses with negative optical power. Because these negatively poweredelements will cause an incident collimated beam to diverge, thepre-scanner optics 420 upstream of the dual-disk scanner introduce acorresponding amount of positive optical power. A collimated beam isconverged by the pre-scanner optics 420 and then diverged by the facets432. The beam is collimated when it exits the dual-disk scanner 430 andis directed to the post-scan imaging lens group 440.

The post-scan imaging lens group 440 is typically of the “F-θ” designclass frequently used for laser line scanners. The “F-θ” post-scan lensgroup 440 has the property that the image is linearly mapped as afunction of the deviated beam scan angle and the scanned line imagemoves nearly constantly as a function of scanner rotation angle. Smallvariances in scan linearity can be corrected electronically (e.g., bypredistorting the image to be displayed) since at least one frame ofdata is typically stored before scanning.

The three element pre-scanner group 420 is designed to accept collimatedinput beams that are inclined at moderate angles to the optical axis ofthis group, due to the scanning of the galvanometer scanner 410 andpossibly also due to the use of multiple optical beams as describedbelow. Accordingly, this group 420 corrects for oblique aberration ofthe input beams (primarily coma aberration). It is also corrected forchromatic aberration. The pre-scanner optics 420 also corrects for theaberrations (including chromatic aberrations) of the two facets 432 whenthey are in their neutral rotational position 432A-B(1).

Because the scanner facets move through the optical path and thereforeintroduce decentered optical surfaces to the optical path, there is alsoa dynamic (changing with rotation angle or with scan time) astigmatism.This dynamic astigmatism can be corrected through the use of asphericsurfaces on the facets 432. For example, the facets can be injectedmolded plastic. The dynamic astigmatism can be corrected while keepingthe corresponding facets identical so they can be produced by a singlemolding tool.

The rotation of the facets through the optical path also introduces adynamic lateral chromatic aberration (chromatic aberration that changeswith rotation angle of the scan disks). This aberration can be correctedby the choice of materials in the post-scan imaging lens group 440.

FIGS. 4-6 show only a single incident optical beam but alternateembodiments can use an array of optical beams. For example, the use of Nvertically arrayed light sources upstream of the galvanometer scanner410 could produce N simultaneous scan lines for each set of facets. Thiscan increase screen brightness and/or reduce vertical scan velocities.It could also be used to permit simultaneous scanning of Red, Green, andBlue color components, for example by simultaneously scanning Red, Greenand Blue optical beams.

FIGS. 7-9 show another example of a HDTV-class display based on adual-disk scanner. The optical train includes anamorphic optics 710, apolygon scanner 720, a relay lens group 730, a pre-scanner lens group740, a dual-disk scanner 750 and a post-scan imaging lens group 760.Only the current facet of the polygon scanner and the scan disks areshown for clarity. In this example, the dual-disk scanner 750 producesthe slow scan (e.g., vertical field scan) and the polygon scanner 720produces the fast scan (e.g., horizontal line scan).

FIG. 7 shows a single optical beam 790 when both the polygon scanner 720and the dual-disk scanner 750 are in their neutral position. FIG. 8illustrates fast scanning by the polygon scanner 720 along the Xdirection and FIG. 9 illustrates slow scanning by the dual-disk scanner750 along the Y direction. The Z direction is along the optical axis.

The anamorphic optics 710 is used to reduce line jitter caused bypyramidal facet errors and bearing wobble in the polygon scanner. Acollimated input beam is incident on the anamorphic optics 710, whichbrings the optical beam to a line focus on the polygon scanner 720. Theline focus is in the plane of the paper in FIG. 8. In other words, theoptical beam is focused in the non-scanning direction for the polygonscanner and is collimated in the scanning direction. The anamorphicrelay lens group 730 images the focused spot in the non-scan directiononto the image surface and simultaneously images the collimated beam inthe scan direction onto the same image surface at the samemagnification. Cylindrical lens surfaces are combined with sphericallens surfaces in both the input lens group 710 and the output lens group730. Jitter effects are significantly reduced with this design becausethe pyramidal error and bearing wobble of the polygon scanner do notaffect the position of the focused line on the facet surface and it isthis fixed spatial location that is relayed by the output lens group 730onto the image surface.

In this particular example, the input lens group 710 includes threeelements: a positive cylindrical-plano element, a positivebi-cylindrical element with the cylinder axis orthogonal to the firstelement and a negative spherical element. The output lens group 730 alsoincludes three elements: a bi-concave negative cylindrical element, apositive spherical element and a plano-cylindrical element. Afterpassing through the output lens group 730, the optical beam iscollimated in both directions but is angularly scanning in thehorizontal plane, as shown in FIG. 8.

This beam next passes through the dual-disk scanning system, whichincludes the pre-scanner optics 740 and the dual-disk scanner 750. Thepre-scanner optics 740 plays a similar role to the pre-scanner optics420 in FIG. 4. It conditions the optical beam for the dual-disk scanner750 and corrects for non-dynamic aberrations introduced by the dual-diskscanner.

The final focusing lens group 760 is shown as a single line in FIGS.7-9. This line represents one of many design forms that can be selectedon the basis of final image dimension constraints such as numericalaperture and field angle. However, the final focusing lens group 760preferably will incorporate materials and surfaces to correct fordynamic lateral chromatic aberration that is introduced by the rotatingfacets 750.

Two-dimensional optical scan systems were described above using specificexamples. This was done for purposes of clarity and the invention is notlimited to these examples. For example, it is not limited to either asingle optical beam or to the same facet replicated over the entire scandisk. Each scan disk 220 contains multiple facets and each set ofcorresponding facets can be designed to produce different scanningmotions. In addition, the bow correction described above need not beused with every facet. In some applications or for some facets, theundesirable effects introduced by conventional bow may be tolerable sothat bow correction is not necessary. At the other extreme, in someapplications, every facet may utilize the bow correction describedabove.

The physical implementations of facets can also vary. For facets thatinclude a separate scan component and some other component (e.g., anoffset component), different designs can place these components indifferent orders within the optical train (e.g., on different sides ofthe scan disk). The scan component and other component can also beintegrated into a single optical component. For example, aberrationcorrection can be integrated with the lens-based scan component andimplemented as an aspheric surface. In addition, although it is usuallydesirable for the optical beams entering and/or exiting thecounter-rotating disk scanner to be collimated, that is not arequirement.

Accordingly, although the description above contains many specifics,these should not be construed as limiting the scope of the invention butmerely as illustrating different examples and aspects of the invention.For example, applications other than displays and scanned imagingsystems will be apparent. Some examples include industrial patterngeneration and printing, including printing documents and labels, or UVimage printing on consumer products. The specific design of thetwo-dimensional optical scan system and also the counter-rotating diskscanner will depend on the application. For example, the wavelength ofthe optical beams will depend in part on the application. Terms such as“optical” and “light” are not meant to be limited to just the visiblerange of the spectrum.

Depending on the application, the two-dimensional scan pattern can alsotake different forms. In many applications, a continuous scan line (orseries of scan lines) is traced repeatedly but offset by some amount oneach trace. The scan lines can also be a series of points rather than acontinuous line, for example if the optical source is pulsed on and offduring scanning or if secondary counter-scanners are used to compressdashes within a scan line into a dot. For example, see FIG. 7B and thecorresponding text of U.S. patent application Ser. No. 10/750,790, “HighSpeed, High Efficiency Optical Pattern Generator Using Rotating OpticalElements,” filed Dec. 31, 2003 by Leonard C. DeBenedictis et al, whichis incorporated herein by reference. Other variations will be apparent.

As another example of different variations, the number of scan disks 220can also vary. The above examples all use a pair of scan disks but thisis not a requirement. Two or more pairs of rotating optical elements canbe used. Alternately, the two-disk designs can be converted tothree-disk designs by “splitting” one of the scan disks into two scandisks. In FIG. 4, the negative lens 432A can be split into two negativelenses with half the power, one placed upstream of the negative lens432B and the other placed downstream of the negative lens 432B.

1. A two-dimensional optical scan system comprising: a counter-rotatingdisk scanner for scanning an optical axis along a first direction; and ascan mechanism optically coupled with the counter-rotating disk scannerfor scanning the optical axis along a second direction that is cross tothe first direction.
 2. The scan system of claim 1 wherein thecounter-rotating disk scanner comprises: a first scan disk and a secondscan disk wherein: each scan disk has a rotational axis and a pluralityof facets that rotate around the rotational axis; facets on the firstscan disk have corresponding facets on the second scan disk; the firstand second scan disks counter-rotate so that corresponding facets rotatethrough the optical axis in synchronization; and the optical axis isscanned along the first direction by the corresponding facets rotatingthrough the optical axis.
 3. The scan system of claim 2 wherein: therotational axes of the two scan disks are offset from each other; theoptical axis is incident on the scan disks at a point located betweenthe two rotational axes; and the first direction is approximatelyparallel to the tangential direction of the scan disks.
 4. The scansystem of claim 2 wherein: the facets on the first and second scan disksinclude lens-like scan components; and the scan components on the firstscan disk have approximately the same optical power as the correspondingscan components on the second scan disk.
 5. The scan system of claim 4wherein the difference in optical power between corresponding scancomponents compensates for a spacing between the scan disks.
 6. The scansystem of claim 4 wherein at least a majority of facets on each scandisk includes a lens-like component with negative power.
 7. The scansystem of claim 4 wherein at least one of the facets on at least one ofthe scan disks includes an aspheric surface.
 8. The scan system of claim7 wherein the aspheric surface corrects for aberrations introduced byrotation of the facet through the optical axis.
 9. The scan system ofclaim 4 further comprising: a pre-scanner lens group that corrects foroptical power introduced by the lens-like scan components.
 10. The scansystem of claim 4 further comprising: a pre-scanner lens group thatcorrects for aberrations introduced by the facets when the facets are ina neutral rotational position.
 11. The scan system of claim 2 whereinthe facets on the scan disks comprise injection molded plastic.
 12. Thescan system of claim 2 wherein a majority of facets on the first scandisk are the same and a majority of facets on the second scan disk arethe same.
 13. The scan system of claim 2 wherein facets on the firstscan disk introduce a first scan line bow and corresponding facets onthe second scan disk introduce a second scan line bow that counteractsthe first scan line bow.
 14. The scan system of claim 1 wherein the scanmechanism comprises: either a piezo-electric scanner or agalvanometer-based scanner.
 15. The scan system of claim 1 wherein thescan mechanism comprises: a polygon scanner.
 16. The scan system ofclaim 1 wherein the scan mechanism comprises: a second counter-rotatingdisk scanner.
 17. The scan system of claim 1 wherein the first directionis a fast scan direction and the second direction is a slow scandirection.
 18. The scan system of claim 1 wherein the first direction isa slow scan direction and the second direction is a fast scan direction.19. The scan system of claim 1 wherein the counter-rotating disk scanneris a reflective counter-rotating disk scanner.
 20. A two-dimensionaloptical display system for scanning an optical beam in two dimensionscomprising: an optical source for generating an optical beam; acounter-rotating disk scanner for scanning the optical beam along afirst direction; and a scan mechanism optically coupled with thecounter-rotating disk scanner for scanning the optical beam along asecond direction that is cross to the first direction.
 21. Thetwo-dimensional optical display system of claim 20 wherein thecounter-rotating disk scanner comprises: a first scan disk and a secondscan disk; wherein: each scan disk has a rotational axis and a pluralityof facets that rotate around the rotational axis; facets on the firstscan disk have corresponding facets on the second scan disk; the firstand second scan disks counter-rotate so that corresponding facets rotatethrough the optical beam in synchronization; and the optical beam isscanned along the first direction as the corresponding facets rotatethrough the optical beam.
 22. The two-dimensional optical display systemof claim 21 wherein: the rotational axes of the two scan disks areoffset from each other; the optical beam is incident on the scan disksat a point located between the two rotational axes; and the firstdirection is approximately parallel to the tangential direction of thescan disks.
 23. The two-dimensional optical display system of claim 21wherein: the facets on the first and second scan disks include lens-likescan components; and the scan components on the first scan disk haveapproximately the same optical power as the scan components on thesecond scan disk.
 24. The two-dimensional optical display system ofclaim 21 wherein facets on the first scan disk introduce a first scanline bow and corresponding facets on the second scan disk introduce asecond scan line bow that counteracts the first scan line bow.
 25. Thetwo-dimensional optical display system of claim 20 wherein: the scanmechanism comprises either a piezo-electric scanner or agalvanometer-based scanner; the scan mechanism is located upstream ofthe disk scanner; and the disk scanner scans the optical beam in a fastscan direction and the scan mechanism scans the optical beam in a slowscan direction.
 26. The two-dimensional optical display system of claim25 further comprising: a pre-scanner lens group located between the scanmechanism and the disk scanner; and a post-scan imaging lens grouplocated downstream of the disk scanner.
 27. The two-dimensional opticaldisplay system of claim 26 wherein: the facets on the first and secondscan disks include lens-like scan components; the scan components on thefirst scan disk have approximately the same optical power as thecorresponding scan components on the second scan disk; and thepre-scanner lens group corrects for optical power introduced by thelens-like scan components.
 28. The two-dimensional optical displaysystem of claim 26 wherein the pre-scanner lens group corrects foraberrations introduced by the facets when the facets are in a neutralrotational position.
 29. The two-dimensional optical display system ofclaim 26 wherein the facets include aspheric surfaces that correct foraberrations introduced by rotation of the facets through the opticalbeam.
 30. The two-dimensional optical display system of claim 26 whereinthe post-scan imaging lens group corrects for aberrations introduced byrotation of the facets through the optical beam.
 31. The two-dimensionaloptical display system of claim 20 wherein: the scan mechanism comprisesa polygon scanner; the polygon scanner is located upstream of the diskscanner; and the polygon scanner scans the optical beam in a fast scandirection and the disk scanner scans the optical beam in a slow scandirection.
 32. The two-dimensional optical display system of claim 31further comprising: a pre-scanner lens group located between the polygonscanner and the disk scanner; and a post-scan imaging lens group locateddownstream of the disk scanner.
 33. The two-dimensional optical displaysystem of claim 32 wherein: the facets on the first and second scandisks include lens-like scan components; the scan components on thefirst scan disk have approximately the same optical power as thecorresponding scan components on the second scan disk; and thepre-scanner lens group corrects for optical power introduced by thelens-like scan components.
 34. The two-dimensional optical displaysystem of claim 32 wherein the pre-scanner lens group corrects foraberrations introduced by the facets when the facets are in a neutralrotational position.
 35. The two-dimensional optical display system ofclaim 32 wherein the facets include aspheric surfaces that correct foraberrations introduced by rotation of the facets through the opticalbeam.
 36. The two-dimensional optical display system of claim 32 whereinthe post-scan imaging lens group corrects for aberrations introduced byrotation of the facets through the optical beam.
 37. The two-dimensionaloptical display system of claim 31 further comprising: an astigmaticlens group located upstream of the polygon scanner; and an astigmaticrelay lens group located between the polygon scanner and the diskscanner.
 38. The two-dimensional optical display system of claim 37wherein the astigmatic lens group focuses an input optical beam to aline focus on the polygon scanner, wherein the line focus is focusedalong the slow scan direction and is collimated along the fast scandirection.
 39. The two-dimensional optical display system of claim 38wherein the astigmatic relay lens group collimates the optical beamalong both the slow scan and fast scan directions.
 40. Thetwo-dimensional optical display system of claim 37 further comprising: apre-scanner lens group located between the astigmatic relay lens groupand the disk scanner for compensating for optical power introduced bythe disk scanner.
 41. The two-dimensional optical display system ofclaim 40 wherein the pre-scanner lens group corrects for monochromaticaberrations introduced by the disk scanner in a neutral rotationalposition.
 42. The two-dimensional optical display system of claim 37wherein the disk scanner includes aspheric surfaces that correct fordynamic off-axis aberrations introduced by rotation of the disk scanner.43. The two-dimensional optical display system of claim 37 furthercomprising: an imaging lens group located downstream of the disk scannerfor projecting an image to be displayed.
 44. The two-dimensional opticaldisplay system of claim 43 wherein the imaging lens groups corrects fordynamic chromatic aberration introduced by rotation of the disk scanner.45. The two-dimensional optical display system of claim 37 wherein theoptical source generates multiple optical beams for simultaneouslydisplaying multiple scan lines.
 46. The two-dimensional optical displaysystem of claim 31 further comprising: an astigmatic lens group locatedupstream of the polygon scanner for focusing an input optical beam to aline focus on the polygon scanner, wherein the line focus is focusedalong the slow scan direction and is collimated along the fast scandirection; an astigmatic relay lens group located between the polygonscanner and the disk scanner, for collimating the optical beam alongboth the slow scan and fast scan directions; a pre-scanner lens grouplocated between the astigmatic relay lens group and the disk scanner forcompensating for optical power introduced by the disk scanner andfurther for correcting monochromatic aberrations introduced by the diskscanner in a neutral rotational position; and an imaging lens grouplocated downstream of the disk scanner for projecting an image to bedisplayed and further for correcting dynamic chromatic aberrationintroduced by rotation of the disk scanner.
 47. The two-dimensionaloptical display system of claim 20 further comprising: an f-theta lensgroup located downstream of the disk scanner and downstream of the scanmechanism.
 48. The two-dimensional optical display system of claim 20wherein the optical source generates multiple optical beams.
 49. Atwo-dimensional scanning optical imaging system comprising: a detectorhaving a field of view; a counter-rotating disk scanner for scanning thefield of view along a first direction; and a scan mechanism opticallycoupled with the counter-rotating disk scanner for scanning the field ofview along a second direction that is cross to the first direction. 50.The two-dimensional optical imaging system of claim 49 wherein thecounter-rotating disk scanner comprises: a first scan disk and a secondscan disk, wherein: each scan disk has a rotational axis and a pluralityof facets that rotate around the rotational axis; facets on the firstscan disk have corresponding facets on the second scan disk; the firstand second scan disks counter-rotate so that corresponding facets rotatethrough the field of view in synchronization; and the field of view isscanned along the first direction as the corresponding facets rotatethrough the field of view.
 51. The two-dimensional optical imagingsystem of claim 50 wherein: the rotational axes of the two scan disksare offset from each other; the field of view is incident on the scandisks at a point located between the two rotational axes; and the firstdirection is approximately parallel to the tangential direction of thescan disks.
 52. The two-dimensional optical imaging system of claim 50wherein: the facets on the first and second scan disks include lens-likescan components; and the scan components on the first scan disk haveapproximately the same optical power as the scan components on thesecond scan disk.
 53. The two-dimensional optical imaging system ofclaim 50 wherein facets on the first scan disk introduce a first bow andcorresponding facets on the second scan disk introduce a second bow thatcounteracts the first bow.
 54. The two-dimensional optical imagingsystem of claim 49 wherein the counter-rotating disk scanner is areflective counter-rotating disk scanner.
 55. The two-dimensionaloptical imaging system of claim 49 further comprising: a pre-scannerlens group located downstream of the disk scanner for compensating foroptical power introduced by the disk scanner and further for correctingmonochromatic aberrations introduced by the disk scanner in a neutralrotational position.
 56. The two-dimensional optical imaging system ofclaim 49 wherein the disk scanner includes aspheric surfaces thatcorrect for dynamic off-axis aberrations introduced by rotation of thedisk scanner.
 57. The two-dimensional optical imaging system of claim 49further comprising: an imaging lens group located upstream of the diskscanner for correcting dynamic chromatic aberration introduced byrotation of the disk scanner.